1. Field of the Invention
The present invention relates to lightweight, portable, self-contained devices to disinfect microbiologically contaminated surfaces and/or equipment and whose operation does not require external power sources. The invention, more specifically, relates to such devices that use chemical methods to generate aqueous solutions of disinfectant, which allow immersion of contaminated objects or are dispensed directly or sprayed as a fine mist onto contaminated surfaces for purposes of reducing or eliminating inhabitant microorganisms.
2. Description of the Prior Art
There is a need for on-site decontamination of surfaces, such as the surfaces of military field feeding equipment, food contact surfaces, food processing or handling equipment, and the surfaces of such foods as melons, strawberries, apples, tomatoes, and other sliced or whole fruits and vegetables. This need cannot be met by the application of mild disinfectant solutions in which the disinfecting agent is not powerful enough (for example, hydrogen peroxide or detergent), the concentration of the disinfectant is too dilute to rapidly kill the target microorganisms in sufficient numbers, or the concentration of the lethal chemical agent is too short-lived due to chemical decomposition. In contradistinction, the power-free generation of chlorine dioxide solution meets the requirements for safe, rapid, and easily deployed decontamination system without altering the quality of foodstuffs while minimizing potential hazards to the user, the environment, or consumer of such food-preparation surfaces and equipment and food.
Powerful disinfectant agents such as chlorine, ozone, or chloramines utilize individualized and often heavy equipment that is electrically powered and require special handling. Ozone rapidly degrades chemically and must be continuously generated through specialized electrically powered equipment to maintain an effective lethal dose. During and after the microbial decontamination process, these chemical agents produce harmful by-products in the workplace atmosphere that potentially can be harmful to human health or the environment. Chlorine is an effective disinfectant of wastewaters, but chlorine is also known to react with organic matter to produce harmful chlorinated by-products or carcinogenic compounds such as carbon tetrachloride. Alcoholic solutions require immersion or scrubbing, which may not reach inaccessible surfaces (such as the calyx region of apples or inside the webbing on the surface of cantaloupe rinds), or may be undesirable when contacting food preparation surfaces, foodstuffs, or other consumables.
The basis of the present invention is a novel method that has been developed for the controlled generation of aqueous solutions of chlorine dioxide without requiring the use of power, or where sparks, flames and fire are hazardous, unattainable, or otherwise undesirable. This method is likewise suitable for a lightweight, portable assembly for disinfection of microbiologically contaminated equipment, surfaces, and actual foodstuffs and involves small amounts of safe, dry chemical reagents. The chemical combination that has been developed for this purpose is convenient to carry and mixes readily with water to controllably generate biocidal chlorine dioxide solutions (U.S. patent application Ser. No. 10/988,442, Publication Number US2006/0097222 A1, Chemical-Combination for Chemical Generation of Disinfectant and Heat, Doona et al.).
This novel chemical combination has been used inside closed containers to generate humid gaseous chlorine dioxide environments (U.S. patent application Ser. No. 11/105,211, Publication Number US2006/0099121 A1, Portable Chemical Sterilizer, Doona et al.). One particular purpose of this technology is the power-free sterilization of medical equipment and surgical instruments in austere environments as may be encountered by military far-forward surgical teams, disaster relief workers, emergency first-responders, or by humanitarian aid workers in third world countries. This technology has also been used under less stringent conditions to eliminate bacterial pathogens such as Listeria monocytogenes and Escherichia coli from the surfaces of tomatoes without discoloring the fruit, or to inactivate the polyphenoloxidase enzyme in sliced apples, thereby preventing enzymatic browning of the cut apple tissue with exposure to ambient oxygen. The container configuration has been generally aimed at having sufficient size and capacity to hold a standard tray of surgical instruments, but the container configuration can be varied without changing the fundamental principles of operation or procedure for achieving target microbial kills.
Large-scale food-handling equipment and food contact surfaces such as counter tops and cutting boards in need of disinfection cannot always be conveniently removed, separated, or inserted into reasonably sized containers for exposure to a chlorine dioxide environment. However, chlorine dioxide can be used to sanitize surfaces that come into contact with food, and thereby prevent the spread of food-borne illnesses through direct contact or through secondary contamination, by developing an alternative method of dispensing, delivering, or contacting the chlorine dioxide to these contaminated surfaces.
Therefore, an object of this invention is to controllably generate aqueous solutions of biocidal chlorine dioxide using the chemical combination described above, and a number of variants thereof, in a manner different from that used to create humid gaseous chlorine dioxide environments in closed containers for purposes of medical sterilization or produce decontamination, also described above. The chemical combination consists of mixtures of prescribed amounts of sodium chlorite (NaClO2), sodium sulfite (Na2SO3), sodium hydrogen ascorbate (C6H7O6Na), and water that react in either batch mode or in continuous-flow processes to generate an aqueous solution of chlorine dioxide. The batch mode generation of aqueous chlorine dioxide solution can involve the use of a container comprising a lightweight, portable, handheld, closable plastic bottle (rigid plastic or flexible plastic pouch material work equally well) and equipped with an adapter to receive a manually-operated trigger sprayer commonly found on ordinary household cleansers. After generation, the aqueous chlorine dioxide solution can be dispensed directly onto the microbiologically contaminated surfaces from the opened plastic bottle or delivered as a fine mist or aerosol by spraying after closing the bottle with the spray device to achieve the intended surface disinfection or decontamination process. Alternatively, the batch mode generation of aqueous chlorine dioxide solution can involve a container comprising an open bucket that either allows for immersion of contaminated objects such as fresh produce into the disinfecting solution, or into which can be immersed sponges or mops to transfer the chlorine dioxide to the target area for cleaning and disinfection. Another alternative comprises continuous-flow systems comprising tubes or continuous-flow stirred tank reactors that are open to a feed of fresh reagents at a controlled rate and that also allow chemical reaction to take place and produce the aqueous chlorine dioxide disinfectant solution that may then be placed into a bucket, bottle, or sprayer device.
As indicated above, to accomplish these objectives, one cannot simply mimic the mixing procedures described in patent application Ser. No. 11/105,211. Rather, one must determine appropriate variants of the novel chemical combination described in U.S. patent application Ser. No. 10/988,442, select an appropriate sprayer device, bottle, or bucket, and develop a mixing procedure. This disclosure details this novel process, apparatus, and procedure for accomplishing an aqueous chlorine dioxide solution for effective disinfection of foodborne or infectious microorganisms contaminating surfaces.
Disinfectants such as chlorine, ethylene oxide, and fluorine-containing interhalogens are stable but highly reactive chemicals that must be transported in bulky, secure containers to ensure safety. While these chemicals can be transported they are not efficacious in food-preparation environments because of their large weight, size, and inconvenient and ineffective methods of application. Traditional methods of generating chlorine dioxide are too cumbersome, too slow, or too hazardous to allow disinfection of surfaces and foodstuffs.
For example, Svoboda et al. U.S. Pat. No. 4,021,585 teaches the spraying of freshly slaughtered meat carcasses with chlorine dioxide solutions for disinfection without bleaching or discoloring the meat surface. However, the chlorine dioxide is generated “with commercially available equipment . . . ,” which would be unsuitable for a kitchen or dining area location, especially those that are transportable for military field feeding, for the reasons indicated above.
Electrochemical methods usually raise the oxidation number of chlorine within a chlorine-containing compound, e.g. oxidizing aqueous chloride solutions, often brines, Rojas, Ser. No. 10/447,572, Publication Number US 2004/0104127. Chemical methods favor the formation of dichlorine gas for this purpose, Jeffries, III et al. U.S. Pat. No. 4,908,188. Alternatively, the oxidation number of chlorine in a chlorine-containing compound can be lowered. For example, reduction of sodium chlorate by hydrogen peroxide, glycerol or sucrose has been suggested, Khan et al. U.S. Pat. No. 6,287,533. These methods require high temperatures and/or catalysts, and are not suitable for safe, rapid generation of chlorine dioxide solutions in a hospital, kitchen or other food processing environment.
Because of chlorine dioxide's potential as a workplace, health clinic or home disinfectant, methods have been developed to circumvent the use of inconvenient and heavy or pressurized cylinder-requiring electrochemical equipment or hazardous strong oxidants such as hypochlorous acid. These methods are based on proton transfer to sodium chlorite by acidification. Acidification-generated chlorous acid disproportionates, producing chloride and chlorate ions and various amounts of chlorine dioxide. The prior art shows that chlorine dioxide so produced can be used for disinfection in food processing plants.
For example, Mason et al. U.S. Pat. Nos. 4,731,193 and 4,889,654 disclose an aqueous foam containing chlorine dioxide for this purpose. The patent claims to mask the odor of chlorine dioxide, because “ . . . its strong, unpleasant odor when dissolved in water makes it impossible to spray at concentrations necessary to achieve sanitation.” Mason et al. do not teach a new method of generating chlorine dioxide. The patent states that “ . . . generating the chlorine dioxide outside the solution and subsequently dissolving it therein” is acceptable. However, in the Mason et al. embodiments that generate the chlorine dioxide in the foam solution, either a water-soluble metal chlorite is acidified, preferably with an organic acid such as citric or oxalic acid, or the chlorite is oxidized by a strong oxidant such as dichlorine or hypochlorous acid. Foam is generated from a surfactant, which may be enhanced with penetrants, non-aqueous solvents, and alkaline cleaners. The odoriferous component in Mason et al. relates to the method of chlorine dioxide generation, which can produce odorous dichlorine and hypochlorous acid gases. In contrast, the present invention yields a dilute aqueous solution of chlorine dioxide that can be dispensed by pouring or spraying a fine mist directly onto and covering all surfaces for purposes of disinfection. Release of gas is minimized, and does not produce a strong or unpleasant odor. The odor, though present, is not pronounced, because of the use of the novel chemical combination (Ser. No. 10/988,442) to controllably produce chlorine dioxide in these circumstances without invoking an acidification process.
The decomposition of chlorous acid is slow and difficult to control. The prior art teaches catalysis and compartmentalization of reagents to speed the reaction and gain some control over it. Girard U.S. Pat. No. 6,764,661 uses compartmentalization and wick means for separating reactants and for transporting water to one or more reactants. The chlorine dioxide is then allowed to diffuse into a separate compartment to constitute the disinfecting solution.
Impregnation of inert zeolite crystals furthers compartmentalization and avoids mixing. Klatte U.S. Pat. No. 6,503,419 teaches impregnation of zeolite crystals with metal chlorite. A second, separate assemblage of zeolite crystals is impregnated with proton-generating species; an acid or a hydrolyzing metal salt such as CoCl2, for example. Activation of the crystals occurs when water is added to the proton-releasing zeolite. Fluid flow carries the acidified solution into the metal chlorite zeolite compartment, where chlorine dioxide gas is generated.
Hamilton et al. U.S. Pat. Nos. 6,602,466 and 6,607,696 teach a method for the controlled delivery of different gases, but take special note of generating and delivering chlorine dioxide gas. These gases cannot be construed as aqueous solutions for reasons mentioned below. Control is exerted by means of successively surrounding one envelope or sachet with another, until an entire sequence of such enclosed pouches-within-pouches has been constructed. This apparatus is claimed to deliver a dose of chlorine dioxide gas to an awaiting volume of water in “ . . . 5 to 15 minutes.” For most food-handling and processing purposes, this apparatus does not provide controlled production and rapid enough access to a chlorine dioxide solution. The different pouch and envelope surfaces, when not ruptured, act as barriers to diffusion, and the control exerted is to slow down, not speed up the process of forming a disinfectant solution. A similar acidification method used for separating reactants from water, Thangaraj et al. U.S. Pat. No. 6,238,643, suffers from the same drawbacks.
The traditional method to increase the rate of a chemical reaction is through catalysis. Catalysts of the acidification method, however, are expensive and short-lasting, Ostgard U.S. Pat. No. 6,399,039, and it is expected that oxidation-reduction reaction catalysts are likewise expensive and have a short useful duration.
Therefore, it is apparent that there is currently no method available that can controllably generate aqueous chlorine dioxide solutions, preferably in a handheld sprayer device, to sanitize feeding equipment, food contact surfaces, and foodstuffs, all of which can harbor infectious pathogens due to reasons of poor hygiene, contact with contaminated foods, or to bio-terrorism or agri-terrorism. What is needed is a method, operating in either batch or continuous-flow, of generating aqueous disinfectant that is convenient, easy to use, and effective at low doses against microbes. The chemical combination specified in Ser. No. 10/988,442 can be used with appropriate modifications to generate aqueous chlorine dioxide in a sprayer device, in other containers (e.g., bottles or buckets), or by a continuous-flow system. Adjusting the amounts of the dry chemical powders and water specified in Ser. No. 10/988,442 to appropriate levels allows for control of the rate of chlorine dioxide production and optimization of the final concentration of chlorine dioxide in aqueous solution in the sprayer apparatus, and a single sprayer device can then be re-used multiple times for a number of different applications, such as decontaminating food processing or feeding equipment, kitchens, sinks, counter tops, bathrooms or latrines, showers, or fresh produce.